LIVERMORE, Calif. - Global warming is already occurring in the United States and the choices Americans make today will determine the severity of its impact in the future, according to a new report released today.
Researchers representing 13 U.S. government science agencies, major universities and research institutes, including Lawrence Livermore National Laboratory, produced the study entitled "Global Climate Change Impacts in the United States."
Benjamin Santer of LLNL's Program for Climate Model Diagnosis and Intercomparison was a lead author of the first chapter, "Global Climate Change."
"This part of the report explains why climate is changing and how we know that we are the ones causing it," Santer said. "Climate change is telling us a consistent story: Humans have had a pronounced effect on global climate."
The most comprehensive report to date on the likely national impact of global climate change provides current information on changes in temperatures, rainfall patterns and sea level, and also focuses on the regional and sectoral effects of these changes.
The study finds that Americans are already being influenced by climate change through extreme weather, drought and wildfire, and details how the nation's transportation, agriculture, health, water and energy sectors will be affected in the future. The study also finds that the current trend in the emission of greenhouse gas pollution is significantly above the worst-case scenario examined in this report.
Santer's chapter finds:
- Human activities have led to large increases in heat-trapping gases over the past century.
- Global average temperature and sea level have increased, and precipitation patterns have changed.
- The global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases. Human "fingerprints" also have been identified in many other aspects of the climate system, including changes in ocean heat content, precipitation, atmospheric moisture and Arctic sea ice.
- Global temperatures are projected to continue to rise over this century; by how much and for how long depend on a number of factors, including the amount of heat-trapping gas emissions and how sensitive the climate is to those emissions.
The emissions responsible for human-induced warming come primarily from the burning of fossil fuels (coal, oil, and gas) with additional contributions from the clearing of forests and agricultural activities.
Global average temperature has risen by about 1.5o Fahrenheit since 1900. By 2100, it is projected to rise another 2o to 10o Fahrenheit. Increases at the lower end of this range are more likely if global heat-trapping gas emissions are cut substantially. If emissions continue to rise at or near current rates, temperature increases are more likely to be near the upper end of the range.
A product of the interagency U.S. Global Change Research Program and led by NOAA, the definitive 190-page report is written in plain language, intended to better inform members of the public and policymakers. It was commissioned in 2007.
"Our report underscores the importance of reducing heat-trapping emissions by comparing impacts that will result from higher versus lower emissions," said Tom Karl, director of NOAA's National Climatic Data Center in Asheville, N.C. and one of the co-chairs of the report. "It shows that the choices made now will have far-reaching consequences."
The report draws from a large body of scientific information, including the set of 21 Synthesis and Assessment reports from the U.S. Global Change Research Program. The government agencies affiliated with the program include the Departments of Agriculture, Commerce, Defense, Energy, Health and Human Services, Interior, State, and Transportation; the Environmental Protection Agency; NASA; National Science Foundation; Smithsonian Institution; and the United States Agency for International Development.
The report is available for download online: http://www.globalchange.gov/usimpacts .